Lake basin evolution of Ordos Basin during Middle-Late Triassic and its origin analysis

Taking Chang 7 of the Triassic Yanchang age as the turning point, the depocenter of Yanchang Lake in Ordos Basin migrated southwestwardly from Wuqi-Fuxian area in Early Triassic to Huachi-Huangling area in Middle-Late Triassic. Affected by the migration, the southwest depositional system and the northeast depositional system developed unsymmetrically. The southwest system was more basinward-extending in Early Taiassic than in Late Triassic, however the northeast system has the opposition condition. The intensive orogenic movement of late Indo-Chinese epoch in western Qinling caused the SW to NE compressive force to Ordos Basin and the vertical uplift of Yinshan region caused the tilt of the northeast part of the Basin. The compressive force and the tilt may be the origin of the depocenter migration and the unsymmetrical development of the south and north depositional systems during Middle-Late Triassic in Ordos Basin.